Device comprising an electric discharge tube having a pentode characteristic



Feb. 17, 1959 E. J. VAN BARNEVELD ET AL 2,874,282

DEVICE COMPRISING AN ELECTRIC DISCHARGE TUBE HAVING A PENTODECHARACTERISTIC Filed Dec. 6, 1954 INVENTOFG EVERT JAN VAN BARNEVELDPETER JOHANNES HUBERTUS JANSSEh U te S ates. P te 0.

DEVICE COMPRISING AN ELECTRIC DISCHARGE TUBE HAVING A r -Nronncnsnnornmsrrc Application December 6, 1954, Serial 'No. 473,362 Claimspriority, application Netherlands December 10, 1953 2 Claims. (Cl.250-27) The invention relates to arrangements comprising an electricdischarge tube having a pentode characteristic and more particularly toarrangements to which a signal s supplied and which comprise a controldevice which is rendered operative by means of an auxiliary signal atinstants at which the signal reaches a reference value, the controldevice with the aid of an integrating network producing a controlvoltage controlling the transmission of the signal.

Such devices may be used for various purposes such as the introductionof the direct current component into television, radar and facsimilesignals or automatic gain control such as, for example, is used intelevision receivers.

According to the invention an input signal, such as a compositetelevision signal including synchronizing pulses is supplied to acontrol electrode of a discharge tube having a pentode characteristicand comprising at least a cathode, a control electrode, a screenelectrode, a suppressor electrode, and an anode; and an auxiliarysignal, such as a synchronizing signal alone, is supplied to anauxiliary electrode which is arranged between the suppressor grid andthe anode and is located substantially outside the primary electroncurrent. This auxiliary electrode exhibits a penetration coefficientsuch that the variation of the anode current is substantially entirelycounteracted. That is to say, the auxiliary electrode does not simplyintercept a certain percentage of the electrons which should go to theanode, thus decreasing the total anode current by the amount of theintercepted electrons; instead, the auxiliary electrode attracts moreelectrons from the cathode region of the tube so that the anode currentremains substantially unchanged. Preferably this auxiliary electrodeconsists of two supporting rods which are located entirely outside theprimary electron current and are interconnected by a narrow metal stripadjacent one of the ends of the electrode system. The width of thisstrip preferably is approximately 10 to 15% of the axial length of theanode, while the penetration coefficient preferably exceeds .05% but isless than .2%

The invention will now be described with reference to the accompanyingdrawing, in which Fig. 1 is a diagram of an arrangement according to theinvention and Figs. 2 and 3 show details of the tube for use in thisarrangement.

In Figs. 1 and 2, the discharge tube of the invention comprises acathode 1, a control grid 2, a screen grid 3, a suppressor grid 4, andan output anode 5, which are arranged in the customary cylindricalelectrode type of structure and are enclosed in a bulb 7. An auxiliaryelectrode 6 is arranged between the suppressor grid 4 and the anode 5 inaccordance with the invention. Electrode 6 consists of a metallic stripsecured to two supporting rods which, as is shown in Fig. 3, are securedto a pair of insulating discs 9 and 10 located at opposite ends of thecylindrical electrode structure. Preferably, the strip 2,874,282Patented Feb. 17, 1955 ICE 6 is arranged at the very end of thestructure, the ar' rangement being such that the penetration coeflicientof the auxiliary electrode is at least .05 but does not exceed .2%. Theterm penetration coeflicient" is defined as the .reciprocal of theamplification factor, or 11., and is' therefore a measure of theinfluence of electrode 6 on the control electrode 3.

In the operation of thecircuit of Fig. 1 a received signal, for examplea detected television signal 13 consisting of a video portion andrepetitive synchronizing pulses,is supplied to the input terminal 11 andthrough a capacitor 12 tothe control grid 2. As is well-known, thissignal comprises reference values, for example during the linesynchronizing pulses, while a further reference value is availableduring the remainder of the re trace intervals, the latter valuecorresponding to the black level.

During the occurrence of the reference value at the control electrode ahighly positive voltage pulse or key pulse signal 14 having a repetitionrate equal to that of the synchronizing pulses in signal 13 is suppliedto the auxiliary electrode 6. Consequently, at this instant an electroncurrent flows to this electrode 6 which may be approximately 1 to 2% ofthe anode curent at this instant. Due to the negative reference voltageat the control grid during the retrace interval the anode current iscomparatively small. The current of electrode 6 is subtracted from theanode current so that the electrode 6 tends to reduce slightly the anodecurrent. However, since the electrode 6 exhibits a certain penetrationcoefficient, the anode current will not be subjected to a permanentdecrease during the entire key pulse 14 but will be subjected to atransient variation of lower amplitude, which is more desirable than acomparatively prolonged stronger decrease of the anode current.

Because the auxiliary electrode 6 is arranged behind the suppressor grid4, its current is substantially independent of the voltage of key pulse14. This current is integrated with the aid of an integrating networkconsistmg of condenser 15 and resistor 16 and the voltage set up acrossthis integrating network is supplied to the control grid 2 throughresistor 17.

If the reference value of the alternating voltage signal at the controlgrid 2 shifts to a higher level, a larger current will flow to theelectrode 6 during each of the pulses 14 with the result that a highernegative voltage will be set up across the integrating network and willbe fed back to reduce the control grid voltage. Consequently, thevariation of the reference value at the control grid is counteracted sothat the level of the reference value at the control grid is renderedsubstantially constant, that is to say a direct current component isintroduced. In a television signal the black level can thus bemaintained constant.

Although only a single embodiment of a tube according to the inventionhas been described, it will be understood -that alternativeconstructions in accordance with the invention are possible.

What is claimed is:

1. A black level control circuit comprising an electron discharge tubehaving a cathode, a control grid, a screen grid, a suppressor grid, ananode, and an auxiliary elecconnected to apply a pulse voltage to saidauxiliaryelec; trode to make said auxiliaryplectrode positiveduring theoccurrence of each of said reference portions of said first signalvoltage whereby the instantaneous current flowing to said auxiliaryelectrode during each of said reference portions is determined by thereference level of the voltage between said. control grid and saidcathode; and a connection between said auxiliary electrode and saidcontrol grid, said connection comprising an integrating circuit toreturn said voltage between said cathode and said control grid tosubstantially the same value during each of said reference portions.

2. A black level control circuit as claimed in claim 7 in which theauxiliary electrode of said electron discharge tube comprises a strip ofconductive material and support rods for said strip, so located withinsaid tube that the support means lie outside of the primary path ofelectron flow between said cathode and said anode and said strip liespartially within said path, the width of said strip being in the rangeof 10 to 15% of the axial length of said anode.

References Cited in the file of this patent V UNITED STATES PATENTS2,143,916 Jonker et a1 Jan. 17, 1939 2,239,677 Iobst Apr. 29, 19412,244,672 Brett June 10, 1941 2,454,377 Curtis Nov. 23, 1948 2,491,932Reitz et a1. Dec. 20, 1949 2,551,057 Schweizer May 1, 1951 2,601,491Baker June 24, 1952 2,656,414 Roschke et al Oct. 20, 1953

